1. Field of the Invention
The present invention relates to small internal combustion engines of the type used with lawnmowers, lawn and garden tractors, snow throwers, other working implements, or small sport vehicles. In particular, the present invention relates to a priming system to aid in starting such engines.
2. Description of the Related Art
Small internal combustion engines typically include a carburetor which mixes liquid fuel with atmospheric air drawn through the carburetor to provide an air/fuel combustion mixture to the engine. One type of carburetor commonly used in small engines includes a throat with a venturi through which air is drawn, and into which fuel is also drawn for mixing with the intake air, as well as a fuel bowl disposed beneath the throat in which a quantity of liquid fuel is stored. A float valve in the fuel bowl meters a supply of fuel into the fuel bowl from a main fuel tank as necessary as the fuel in the fuel bowl is consumed.
Additionally, such carburetors typically include a manually operable priming mechanism, such as a priming bulb which is pressed by an operator to pressurize the air space above the fuel in the fuel bowl and to force a quantity of priming fuel from the fuel bowl into the carburetor throat for mixing with the intake air which is drawn into the carburetor. The priming fuel is in excess of the amount of fuel which is normally supplied for mixing with the intake air to form the combustion mixture, such that a rich air/fuel mixture is initially supplied to the engine to aid in engine starting. After the engine starts, the priming fuel is consumed, and mixing of the air/fuel mixture is thereafter controlled by the fuel metering system of the carburetor during running of the engine.
The foregoing type of priming mechanisms for carburetors requires an operator to manually press the priming bulb to prime the engine. If the operator does not press the bulb enough times, or if the operator fails to press the priming bulb altogether, pressure will not be built up within the fuel bowl of the carburetor to the extent necessary to supply priming fuel to aid in engine starting. Therefore, difficulty may be encountered in starting the engine. Conversely, if the priming bulb is pressed by an operator too many times, an undesirably large amount of priming fuel may be supplied, which could flood the engine.
Additionally, many carburetors for small engines also include a choke feature, such as a choke valve, which is manually actuated by the operator during engine starting to further enrich the air/fuel mixture initially supplied to the engine. However, until the choke feature is manually deactivated by the operator, the carburetor will continue to supply an enriched air/fuel mixture to the engine after the engine has started, which could flood the engine. Therefore, the operator must remember to deactivate the choke feature after the engine begins to run in order to prevent the engine from flooding.
In small internal combustion engines, the reciprocation of the piston within the engine cylinder at cranking and running speeds of the engine creates positive and negative pressure fluctuations, or positive and negative pressure pulses, within the crankcase of the engine. Additionally, when the piston reciprocates within the cylinder, a small portion of the gases within the combustion chamber of the engine may pass between the piston and the cylinder bore, particularly during the compression stroke of the piston. Therefore, during running of the engine, although there are both positive and negative pressure pulses in the engine crankcase, the average pressure within the crankcase is positive. A portion of the positive pressure within the crankcase must be vented during running of the engine, typically through a one-way breather check valve in the engine crankcase. Positive pressure pulses from the breather valve are typically “recirculated” to the intake system of the engine, for mixing with the intake air and fuel for combustion within the engine.
It is desirable to provide a priming system for use in small internal combustion engines having carburetors which is an improvement over the foregoing.